Apnea is defined in Stedman's Medical Dictionary, 26.sup.th Edition, Williams and Wilkins (1995), as the absence of breathing. There are a number of disorders associated with apnea, which are characterized by interrupted breathing in which a person stops breathing long enough to decrease the amount of oxygen and increase the amount of carbon dioxide in the blood and brain. Each type of apnea involves the absence of airflow at the nose or the mouth, typically for at least 10 seconds.
Various apnea disorders exist, including: central apnea, which results from medullary depression and inhibits respiratory movement; deglutition apnea, which is the inhibition of breathing during swallowing; obstructive or peripheral apnea, which is either a result of obstruction of air passages or inadequate respiratory muscle activity; sleep apnea, which is central and/or obstructive apnea during sleep; and sleep induced apnea, which results from failure of the respiratory center to stimulate adequate respiration during sleep.
Obstructive apneas usually occur in obese men and are much less common in women. The obesity, perhaps in combination with aging body tissues and other factors, leads to narrowing of the upper airways. Tobacco smoking, excessive alcohol use, and lung diseases, such as emphysema, increase the risk of developing obstructive apneas.
For those suffering from sleep apnea, quitting smoking, avoiding excessive use of alcohol, and losing weight are commonly the first behavioral steps for treating the disorder. In order to inhibit or avoid apnea, heavy snorers and people who often choke in their sleep should not take tranquilizers, sleep aids, or other sedating drugs.
Sleep apnea is one of the most common forms of apnea. Rarely, a person who has severe sleep apnea needs a tracheostomy, a surgical procedure that creates a permanent opening into the windpipe through the neck. Sometimes other surgical procedures are performed to widen the upper airway and alleviate the problem. However, such extreme measures are seldom needed and never desired.
Apnea can also be treated by non-invasive means by administering to a patient a therapeutic agent. U.S. Pat. No. 5,075,290 discloses the medical treatment of obstructive sleep apnea and associated symptoms, such as snoring, by the administration of the nucleoside uptake blocker, dipyridamole, during sleep. U.S. Pat. Nos. 5,502,067 and 5,407,953 disclose a method of treating sleep apnea, hyponea and snoring in a human patient by administering a pilocarpine compound. U.S. Pat. No. 5,422,374 discloses a method of treating sleep apnea by the administration of ubidecarenone to a patient. U.S. Pat. No. 5,356,934 discloses a method of employing (R)-fluoxetine to treat sleep apnea.
Bulimia nervosa, or bulimia, is a disorder described in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, American Psychiatric Association, 1996 ("DSM-IV"), which is characterized in part by recurrent episodes of binge eating during which the patient experiences a loss of control resulting in over eating and self-induced vomiting. The disorder primarily afflicts females of upper and middle socioeconomic status, especially college-age women.
Currently, two approaches for treating bulimia are used: cognitive-behavioral and pharmacological. Traditional pharmacological treatments involved antidepressants. More recent research into the fundamental causes of bulimia, however, has suggested other pharmacological treatments. In particular, some researchers have argued that the pathophysiological characteristics driving the behaviors characteristic of bulimia involve an increase in the basal tone of the vagal nerve, and have suggested that racemic ondansetron may be useful for the treatment of bulimia. Faris, P. L. et al., Biol. Psychiatry, 32:462-466 (1992); Dumuis et al., N.S. Arch. Pharmacol., 340:403-410 (1989).
Cisapride, chemically named cis-4-amino-5-chloro-N-[1-[3-(4-fluorophenoxy)propyl]-3-methoxy-4-piperidi nyl]-2-methoxybenzamide, is a benzamide derivative, the parent compound being metoclopramide. Schapira et al., Acta Gastroenterolog. Belg., LIII:446-457 (1990). Benzamide derivatives have several prominent pharmacological actions due to their effects on neuronal systems modulated by the neurotransmitter serotonin.
Because of their modulation of the serotonin neuronal system in the gastrointestinal tract, many benzamide derivatives are effective antiemetic agents and are commonly used to control vomiting during cancer chemotherapy or radiotherapy. Costall et al., Neuropharmacology, 26:1321-1326 (1987). This action is almost certainly the result of an ability to block serotonin at specific sites, particularly type-3 5-hydroxytryptamine (5-HT.sub.3) receptors. Clarke et al., Trends in Pharmacological Sciences, 10:385-386 (1989). In theory, chemotherapy and radiation therapy can induce nausea and vomiting by damaging enterochromaffin cells in the gastrointestinal tract. As a result, the neurotransmitter serotonin is released and stimulates both afferent vagal nerve fibers (thus initiating the vomiting reflex) and serotonin receptors in the chemoreceptor trigger zone of the area postrema region of the brain. The anatomical site for this action of the benzamide derivatives, and whether such action is central (CNS), peripheral, or a combination thereof, remains unresolved. Barnes et al., J.Pharm. Pharmacol., 40:586-588 (1988).
Racemic cisapride is used primarily to treat gastroesophageal reflux disease ("GERD"), which is characterized as the backward flow of the stomach contents into the esophagus. Cisapride is commercially available as the racemic mixture of the cis diastereomeric enantiomers of cisapride known as PROPULSID.RTM..
The co-administration of racemic cisapride with other therapeutic agents causes inhibitory problems with the metabolism of cisapride by the liver. For example, ketoconazole has a pronounced effect on cisapride kinetics resulting from the inhibition of the metabolic elimination of cisapride and leads to an 8-fold increase of the steady-state plasma levels. Physician's Desk Reference.RTM., 52.sup.nd Edition, Medical Economics Co., Inc., 1998. Interaction of racemic cisapride and other therapeutic agents can also potentiate cardiovascular side effects, such as cardiotoxicity. This potentiation occurs when other drugs present in the patients system interfere with the metabolism of cisapride, thereby building up racemic cisapride in the body.
These interactions are a significant drawback to the use of racemic cisapride; in particular, because racemic cisapride is often used before, with or immediately after another therapeutic agent. In addition, administration of racemic cisapride to a human has been found to cause adverse effects such as cardiac arrhythmia, including ventricular tachycardia, ventricular fibrillation, Q.sub.T prolongation, and torsades de pointes, central nervous system ("CNS") effects, increased systolic pressure, interactions with other drugs, diarrhea, abdominal cramping and cardiac depression.
Racemic cisapride is almost completely absorbed after oral administration to humans, but bioavailability of cisapride is only 40-50% due to rapid first-pass metabolism in the liver. Van Peer et al., in Progress in the Treatment of Gastrointestinal Motility Disorders: The Role of Cisapride, Proceedings of a Symposium in Frankfurt, Germany, November 1986, Excerpta Medica, A. G. Johnson and G Lux Eds., Amsterdam, pp. 23-29 (1988). More than 90% of a dose of racemic cisapride in humans is metabolized mainly by oxidative N-dealkylation of the piperidine nitrogen or by aromatic hydroxylation occurring on either the 4-fluorophenoxy or benzamide rings. Meuldermans et al., Drug Metab. Dispos., 16(3):410-419 (1988); and Meuldermans et al., Drug Metab. Dispos., 16(3):403-409 (1988). Norcisapride, chemically named 4-amino-5-chloro-N-(3-methoxy-4-piperidinyl)-2-methoxybenzamide, is a metabolite of cisapride.
Recently, investigators have reported that the optically pure (+) stereoisomer of the cisapride metabolite norcisapride exhibits many of the useful characteristics, but without certain of the attendant side effects of racemic cisapride. U.S. Pat. No. 5,739,151 discloses methods of eliciting an antiemetic effect by administration of (+) norcisapride.
It is desirable to provide safe and effective methods of preventing, treating, or managing apnea, apnea disorders, bulimia nervosa and related disorders, or symptoms thereof, particularly a treatment that allows the patient to undergo other related therapies without adverse effects or drug-drug interactions.